I investigated the population attributes and habitat selection of mountain beaver (Aplodontia rufa) recolonizing clearcuts in the Coast Range mountains of Polk and Lincoln counties, Oregon between June 1989 and August 1990. The population characteristics of colonizing mountain beaver were evaluated in 12 stands of 3 types: 1-year-old clearcuts assumed to be inhabited entirely by immigrants, 4- to 5-year-old clearcuts inhabited by immigrants and their descendants, and 40- to 60-year-old forest stands assumed to support stable mountain beaver populations. Mountain beaver rapidly recolonized vacant habitat created by previous trapping efforts; after only 1 year, densities in clearcuts were statistically indistinguishable from forest sites (P = 0.7). Populations in 1-year-old clearcuts had more juveniles (P = 0.03) and had a female bias (P = 0.02) when compared with the predominantly adult male populations in the other two stand types. Individuals from clearcuts were heavier than those from forest sites (P < 0.05). Approximately half of the juvenile females in clearcuts reproduced; no juvenile females were found to be reproductively active in forest stands. Among juvenile females that conceived, those in 1-year-old clearcuts had larger litter sizes than those in 4- to 5-year-old clearcuts (P < 0.05). The 8 clearcuts were used to identify habitat features selected by recolonizing mountain beaver. Clearcuts were colonized irrespective of distances < 400 m from edge (R² = 0.01). Six habitat variables were selected by stepwise logistic regression model colonized versus non-colonized habitat. Mountain beaver selected areas with high amounts (<25-cm) and large (>25-cm) woody debris, forage plants, and uprooted stumps; they were likely to colonize areas that had highly penetrable (soft) soils and areas near drainages. The logistic function that included these 6 variables had a correct classification rate of 85% based on a jackknife procedure. Forest managers may find these habitat features useful in predicting mountain beaver recolonization and damage. / Graduation date: 1992